The present invention relates generally to trace gas detection and more specifically to cavity enhanced absorption spectroscopy systems and methods for measuring trace gases.
A majority of present instruments capable of implementing cavity ring down absorption spectroscopy methods do not use, or are unable to effectively use, optical feedback to couple a laser to a cavity. This has consequences. For free decay rate cavity ring down spectroscopy (CRDS) methods, poor injection of the laser light to the cavity is achieved. As a result, the ring down rate is rather low (e.g., on the order of hundreds of Hertz). In the case of the phase shift cavity ring down absorption spectroscopy, the laser-cavity injection is also poor, causing additional noise in the measured signals. Also, for both decay rate and phase shift CRDS methods, the laser light coupled to the cavity has a complex frequency-phase characteristic, caused by a phase noise of the laser. The dynamic of the light emitted from the cavity is affected by interference between different frequency components of the light excited in the cavity. That causes an additional noise in the measurements.
Accordingly, there is a need for systems and methods for trace gas detection using a resonance optical cavity with improved performance, e.g., reduced noise and improved precision and accuracy, including cavity ring down spectroscopy systems and methods.